1. Field of the Invention:
The present invention relates to novel ceric oxide particulates having improved morphological characteristics, and to a process for the production of such novel ceric oxide particulates.
As utilized herein, by the term "specific surface" is intended the BET specific surface determined by the Brunauer-Emmett-Teller method described in Journal of the American Chemical Society, 60, 309 (1938).
2. Description of the Prior Art:
Ceric oxide, either alone or in admixture with other metallic oxides, is known to this art, e.g., as a catalyst for the synthesis, in particular, of methanol [C. R. Seances, Acad, Sci., Ser. 2, 292 (12), 883-5 (1981)] or for the treatment of residual gases (published Japanese Patent Application No. 76/62 616).
In order to exhibit good catalytic activity, it is desirable that the ceric oxide have the greatest specific surface possible.
The ceric oxide described in published French Application No. 2,559,754 has a specific surface of at least 85.+-.5 m.sup.2 /g after calcination at a temperature of from 350.degree. to 450.degree. C. It preferably has a specific surface of from 100 to 130 m.sup.2 /g after calcination at a temperature of from 400.degree. to 450.degree. C. This particular ceric oxide is prepared by the hydrolysis of an aqueous solution of ceric nitrate in a nitric acid medium, followed by separation of the precipitate thus formed, washing, optional drying, and then calcination at a temperature of from 300.degree. to 600.degree. C. The product ceric oxide has a large specific surface, but low porosity, as the micropores have an average diameter of from 10 to 20 .ANG. and a total pore volume on the order of 0.02 cm.sup.3 /g.
Another ceric oxide known to the prior art (published French Application No. 2,559,755) has a specific surface of at least 85.+-.5 m.sup.2 /g after calcination at a temperature of from 350.degree. to 500.degree. C. and preferably a specific surface of from 150 to 180 m.sup.2 /g after calcination at a temperature of from 400.degree. to 450.degree. C. Such ceric oxide is produced by precipitating a basic ceric sulfate, by reacting an aqueous solution of ceric nitrate with an aqueous solution containing sulfate ions, separating the precipitate thus formed, washing and optionally drying it, and then calcining it at a temperature of from 300.degree. to 500.degree. C. The ceric oxide prepared in this manner has a large specific surface, a porosity distribution such that the pore diameters range from 10 to 200 .ANG., and a total pore volume of approximately 0.15 m.sup.3 /g. It also contains an amount of residual sulfate ions and, therefore, can only be selectively used for catalysis.